The present invention relates to a system for smoothing or spreading transitions between regions of an image transmitted by a television signal which are processed in a first way and those which are processed in a second different way.
Processing of standard television signals, (such as NTSC or PAL), which represent images, is often changed to adapt to the environment of the signal. This adaptive processing can result in some regions of an image being processed in one way and other adjoining regions being processed in a different way. If the processing differences can be perceived by a viewer, the different regions, and the transition between them, can be discerned, and image quality is degraded.
For example, when separating chrominance and luminance components from the composite video signal, a frame comb filter may be used. As long as there is not change in the image over a frame time interval, the luminance and chrominance components can be completely separated. If the scene changes over the frame time interval, then some color information will be present in the separated luminance component and some brightness information will be present in the chrominance component.
A line comb filter will also separate the luminance and chrominance components from the composite video signal and does not produce significantly degraded component signals in the presence of image motion. However, a line comb filter reduces the vertical resolution of the reproduced image relative to a frame comb filter. In addition, in locations where a vertical transition occurs, an image processed by a line comb filter may be degraded due to color information being introduced into the luminance component, producing an image artifact known as hanging dots; and brightness information being introduced into the chrominance, producing incorrect colors in the neighborhood of the transition.
The television signal may be adaptively processed by detecting the presence or absence of image motion. In regions in which the image is stationay, the frame comb filter is used, and in regions in which the image is changing, the line comb filter is used.
Another example of such adaptive processing is an adaptive double-scanned non-interlaced scan converter. In such a converter, interstitial lines are displayed between lines of the current field. The interstitial lines may be those from the preceding field, however, in such presence of image changes, visible artifacts, such as serrated edges, occur. The interstitial lines may also be interpolated from lines within the current field, but the vertical resolution is reduced and line flicker may occur. In regions in which image changes are detected, intrafield interpolated interstitial lines are displayed and field-delayed interstitial lines are displayed otherwise.
Yet another example is an adaptive peaking circuitry in which regions having relatively high noise are processed with a relatively low peaking factor and regions having relatively low noise are processed with a relatively high peaking factor.
In all of the above examples, the processing of the television signals is changed in response to the value of an estimated parameter of the image. The parameter is motion in the case of luminance/chrominance separation and double scanning non-interlaced conversion, and it is the relative level of noise in the case of the peaking. Differently processed regions, and noticeable boundaries between those regions where the parameter is present and where it is absent is an undesirable artifact introduced by the above types of adaptive processing. It is desirable to reduce the visibility of this artifact in such systems and thereby improve the perceived quality of the image.
In accordance with the invention described in U.S. Pat. No. 4,868,650, issued on Sept. 19, 1989, to H. J. Weckenbrock, a parameter of the composite video signal is estimated for points in the image. A control signal is then generated based on the parameter. This control signal may be used to control the selection of processing modes. The value of the control signal is then spread symmetrically in a gradually decreasing manner around the region in which the control signal is generated in at least one direction. This generates a region in which the processing gradually changes from a region in which one type of processing is performed to that in which the other type of processing is performed.